This invention relates to a method of producing a solution containing D-ribose by epimerizing a solution containing D-arabinose.
D-ribose is a compound which is important as a constituent of nucleic acid, or as a material for synthesizing vitamin B.sub.2. It is known that D-ribose can be produced by extraction from natural matter, fermentation by a micro-organism, or chemical synthesis from furan or glucose. All of these methods, however, are complicated and have a low yield.
The production of D-ribose on an industrial basis has usually been carried out by a method comprising oxidizing D-glucose with oxygen in an aqueous alkali solution to form D-arabonic acid, separating it in the form of a calcium salt, heating it in an aqueous alkali solution for epimerization to form D-ribonic acid, separating it in the form of a metal salt, such as mercury or zinc salt, lactonizing it into D-ribonolactone, and reducing it with a sodium amalgam into D-ribose. The heating of D-arabonic acid in an aqueous alkali solution forms a mixture having an equilibrium D-arabonic acid to D-ribonic acid ratio of 70:30. It is impossible to obtain any D-ribonic acid proportion exceeding 30%. This method is inconvenient to the use of a large quantity of mercury for amalgam reduction.
Bilik et al. reported the epimerizability of various saccharides in an aqueous solution in the presence of a molybdic acid catalyst, including, for example, the epimerizability of about 33% of L-arabinose into L-ribose (Czechoslovak Pat. No. 149,472; Chemical Abstracts, 81, 78189K). A method based on this report was proposed, and comprises oxidizing D-gluconic acid, instead of converting it to D-arabonic acid and D-ribonic acid, converting D-gluconic acid to D-arabinose with hypochlorous acid, and epimerizing D-arabinose to D-ribose in an aqueous solution in the presence of a molybdic acid VI compound as a catalyst (Japanese Laid-Open Patent Specification No. 164699/1980). This method achieves an epimerization ratio (ratio of ribose in an equilibrium mixture) of only about 25%, but is superior to the method hereinbefore described in that it does not use mercury, and requires only a fewer steps. In order to facilitate the separation of molybdic acid from an aqueous solution upon completion of an epimerization reaction using molybdic acid (molybdic acid VI compound) as a catalyst, there has been proposed the use of an ion exchange resin carrying molybdic acid instead of molybdic acid (Japanese Patent Publication No. 40700/1981), or the use of an ion exchange fiber carrying molybdic acid (Japanese Laid-Open Patent Specification No. 76894/1980 disclosing an epimerization ratio of 30.6% from D-arabinose to D-ribose, and Japanese Laid-Open Patent Specification No. 54197/1982 disclosing an epimerization ratio of 27.2% from D-arabinose to D-ribose).
It is known that the heating of L-arabinose in dimethylformamide in the presence of dioxobis(2,4-pentane-dionoto-0, O'-)molybdenum (VI) achieves epimerization of 36% thereof to L-ribose [Abe et al.: Chemical and Pharmaceutical Bulletin, 28, 1324 (1980)].